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Journal Article

Volume Reduction of SCR Catalyst Using Zeolite-Base Honeycomb Substrate

The method of converting NOx with urea SCR is an effective solution for complying with the stringent NOx emission legislations of the future, particularly in the case of heavy duty diesel vehicles. In order to broaden the freedom of SCR catalyst design and volume design, a honeycomb structure formed with metal ion exchanged zeolite (NCH: New Concept Honeycomb) and for comparison a wash-coat type structure (conventional catalyst) were prepared. The possible range of catalyst volume reduction in NCH was investigated by comparative measurement of NH₃ adsorption distribution, consumption behavior of adsorbed NH₃ within the structures, and of space velocity and NO₂/NOx dependence of NOx conversion efficiency. In addition, from NEDC evaluation in an engine bench, it was found that combining urea injection logic suitable for NCH results in equal or higher NOx conversion efficiency and NH₃ slip characteristics with only 1/2 the volume of conventional catalyst structure.
Technical Paper

Validation of a Model and Development of a Simulator for Predicting the Pressure Drop of Diesel Particulate Filters

As demand for wall-flow Diesel Particulate Filters (DPF) increases, accurate predictions of DPF behavior, and in particular their pressure drop, under a wide range of operating conditions bears significant engineering applications. In this work, validation of a model and development of a simulator for predicting the pressure drop of clean and particulate-loaded DPFs are presented. The model, based on a previously developed theory, has been validated extensively in this work. The validation range includes utilizing a large matrix of wall-flow filters varying in their size, cell density and wall thickness, each positioned downstream of light or heavy duty Diesel engines; it also covers a wide range of engine operating conditions such as engine load, flow rate, flow temperature and filter soot loading conditions. The validated model was then incorporated into a DPF pressure drop simulator.
Technical Paper

The NH3-SCR Reaction Performance with Fe/Zeolite Based Catalytic Honeycomb Substrate

Stringent NOx emission legislation accelerates the study of NOx aftertreatment. Urea-SCR system which is one of promising NOx reduction measures has been widely studied and been put to practical use not only for heavy duty vehicles but also passenger cars. As SCR catalyst, although use of zeolite ion-exchanged with transition metals (M/zeolite) has been under intense investigation, in particular, NOx conversion performance at low temperatures are still a challenging problem. Increasing the number of active sites is one of countermeasures to solve the problem. In this study, a catalytic honeycomb substrate mainly comprised of M/zeolite (NCH structure) and a conventional wash coated type catalyst(conventional structure) were prepared, respectively. To clarify the advantage of NCH structure, a relationship between NH3 adsorption and NOx conversion of the NCH structure and of the conventional structure were evaluated in both synthetic gas bench and engine bench.
Technical Paper

Study on the Filter Structure of SiC-DPF with Gas Permeability for Emission Control

The pore structure of DPF (Diesel Particulate Filter) is one of the key factors in contributing the fuel consumption and the emission control performance of a vehicle. The pressure loss of mini samples (1 in. in diameter, 2 in. in length) with various pore structures was measured at relatively low filtration velocity (< 5 cm/sec). Then the obtained data were evaluated by using an index of “permeability”. As a result, among the parameters which characterize the pore structure, it was found that the size of the pore diameter and the sharpness of pore distribution were the most contributing factors in reducing pressure loss which in turn is related to the fuel consumption performance when the cell structure was fixed. On the other hand, it was found that the gas permeability was not affected significantly by any parameter when the catalyst was coated because the coating caused a broadening of the pore distribution.
Technical Paper

Study on Filter Substrate Structure for Lower Backpressure and Higher Regeneration Performance

The trade-off between NOx and particulate matter (PM) has been a technological challenge with respect to diesel engine emissions. However, the practical use of diesel particulate filters (DPF) has made diesel emission control possible, in which NOx emissions are reduced through engine control and nearly all emitted PM is completely removed by DPF from diesel exhaust emissions. This has helped to contribute to laying the foundation for pursuing of the high theoretical thermal efficiency of diesel engines. However, it is also a fact that such emission controls have resulted in considerable impairments on the original and greatest advantages of diesel engines. This includes fuel penalties with accompanying increases in fuel consumption caused by pressure losses due to the attachment of the DPF itself and the accumulation of PM in the DPF, as well as fuel losses that occur when fuel is used to regenerate collected PM.
Technical Paper

Study on Catalyzed-DPF for Improving the Continuous Regeneration Performance and Fuel Economy

It is a big challenge how to satisfy both the purification of exhaust gas and the decrease of fuel penalty, that is, carbon-dioxide emission. Regarding the Diesel Particulate Filter (DPF) applied in the diesel after-treatment system, it must be effective for lowering the fuel penalty to prolong the interval and reduce the frequency of the DPF regeneration operation. This can be achieved by a DPF that has high Particulate Matter (PM) mass limit and high PM oxidation performance that is enough to regenerate the DPF continuously during the normal running operation. In this study, the examination of the pore structure of the wall of a DPF that could expand the continuous regeneration region in the engine operation map was carried out. Several porous materials with a wide range of pore structure were prepared and coated with a Mixed Oxide Catalyst (MOC). The continuous regeneration performance was evaluated under realistic conditions in the exhaust of a diesel engine.
Technical Paper

Spatial Non-Uniformities in Diesel Particulate Trap Regeneration

Diesel particulate trap regeneration is a complex process involving the interaction of phenomena at several scales. A hierarchy of models for the relevant physicochemical processes at the different scales of the problem (porous wall, filter channel, entire trap) is employed to obtain a rigorous description of the process in a multidimensional context. The final model structure is validated against experiments, resulting in a powerful tool for the computer-aided study of the regeneration behavior. In the present work we employ this tool to address the effect of various spatial non-uniformities on the regeneration characteristics of diesel particulate traps. Non-uniformities may include radial variations of flow, temperature and particulate concentration at the filter inlet, as well as variations of particulate loading. In addition, we study the influence of the distribution of catalytic activity along the filter wall.
Technical Paper

Soot Oxidation Kinetics in Diesel Particulate Filters

Direct catalytic soot oxidation is expected to become an important component of future diesel particulate emission control systems. The development of advanced Catalytic Diesel Particulate Filters (CDPFs relies on the interplay of chemistry and geometry in order to enhance soot-catalyst proximity. An extensive set of well-controlled experiments has been performed to provide direct catalytic soot oxidation rates in CDPFs employing small-scale side-stream sample exposure. The experiments are analyzed with a state-of-the-art diesel particulate filter simulator and a set of kinetic parameters are derived for direct catalytic soot oxidation by fuel-borne catalysts as well as by catalytic coatings. The influence of soot-catalyst proximity, on catalytic soot oxidation is found to be excellently described by the so-called Two-Layer model, developed previously by the authors.
Technical Paper

Soot Loading Estimation Accuracy Improvement by Filtration Layer Forming on DPF and New Algorithm of Pressure Loss Measurement

A diesel particulate filter (DPF) is a key component for reduction of engine soot emission. The soot collected in the DPF is periodically burned off, so-called DPF regeneration, and a behavior of the pressure drop increased by the soot loading is generally utilized to estimate the amount, which must be a trigger of the regeneration. However, it is said that the estimation of the soot loading amount has considerable dispersion caused by two main reasons. One is hysteresis of the transient pressure drop resulted from the combination of so-called deep-bed and cake filtration modes. The other is a fluctuation of exhaust gas temperature and flow rate as well as a pulsation from the engine. In this study, the accurate estimation method of the soot amount accumulated in the DPF was proposed in combination with filtration layers (FLs) technology and a new algorithm based on fast Fourier transform (FFT) technology.
Technical Paper

Simulation of Triangular-Cell-Shaped, Fibrous Wall-Flow Filters

In the present work we apply a computational simulation framework developed for square-cell shaped honeycomb Diesel Particulate Filters to study the filtration, pressure drop and soot oxidation characteristics of recently developed triangular-cell-shaped, high porosity wall-flow filters. Emphasis is placed on the evaluation of the applicability and adaptation of the previously developed models to the case of triangular channels. To this end Computational Fluid Dynamics, asymptotic analysis, multichannel and “unit-cell” calculations are employed to analyze filter behavior and the results are shown to compare very well to experiments available in the literature.
Technical Paper

SiC Diesel Particulate Filter Application to Electric Heater System

A heater type automatic regeneration system able to be mounted on an automobile has been developed by utilizing the characteristics of SiC-DPF (Diesel Particulate Filters made of Silicon Carbide). In this development, in order to apply the system to wide applications, the main objective was to focus on reducing the regenerating electric power consumption. For the reduction of the power consumption, realization of a low pressure drop system effect by making the DPF structure high density and improvement of the axial insulation, controlling the gas flow velocity by a general purpose exhaust brake, saving of the electric power by using a DC heater driver utilizing MOSFETs (Metal Oxide semi-conductor field-effect transistor). As a result, a SiC-DPF heater unit usable in wide range of applications has successfully been developed.
Technical Paper

Post Oxidation Study During Secondary Exhaust Air Injection for Fast Catalyst Light-Off

To comply with ever more stringent emission limits, engineers are studying and optimising gasoline engine start-up and warm-up phases. Secondary air injection (SAI) represents one option to reduce emissions by post-oxidizing products of a rich combustion like HC, CO and H2. With this approach, the faster catalytic converter light-off allowed by the increase in exhaust temperature leads to a significant HC emissions reduction. All the mechanisms involved in post oxidation downstream of the exhaust valve are not well-known. In order to achieve substantial improvements, various SAI strategies were studied with a conventional PFI gasoline engine. Tests have been carried out both on steady-state running conditions and on transient warm-up phases at engine test bench. Various specific experimental devices and methodologies were developed. For example, the use of fast HC and temperature measurements is coupled with exhaust gas flow rate modeled with system simulation.
Technical Paper

Persistent Particle Number Emissions Sources at the Tailpipe of Combustion Engines

The more and more stringent regulations on particle emissions at the vehicle tailpipe have led the car manufacturers to adopt suitable emissions control systems, like particulate filters with average filtration efficiency that can exceed 99%, including particulate mass (PM) and number (PN). However, there are still some specific operating conditions that could exhibit noticeable particle number emissions. This paper aims to identify and characterize these persistent sources of PN emissions, based on tests carried out both at the engine test bench and at the chassis dynamometer, and both for Diesel and Gasoline direct injection engines and vehicles. For Diesel engines, highest particle numbers were observed downstream of the catalyzed DPF during some operation conditions like engine warm up or filter regeneration phases. PN could be 50 times higher during the warm up phase and can reach as much as 2000 to 3000 times more during the regeneration phase compared to normal operation.
Journal Article

Performance Assessment of a Multi-Functional Reactor Under Conventional and Advanced Combustion Diesel Engine Exhaust Conditions

Current progress in the development of diesel engines substantially contributes to the reduction of NOx and Particulate Matter (PM) emissions but will not succeed to eliminate the application of Diesel Particulate Filters (DPFs) in the future. In the past we have introduced a Multi-Functional Reactor (MFR) prototype, suitable for the abatement of the gaseous and PM emissions of the Low Temperature Combustion (LTC) engine operation. In this work the performance of MFR prototypes under both conventional and advanced combustion engine operating conditions is presented. The effect of the MFR on the fuel penalty associated to the filter regeneration is assessed via simulation. Special focus is placed on presenting the performance assessment in combination with the existing differences in the morphology and reactivity of the soot particles between the different modes of diesel engine operation (conventional and advanced). The effect of aging on the MFR performance is also presented.
Technical Paper

Multichannel Simulation of Soot Oxidation in Diesel Particulate Filters

In recent years advanced computational tools of Diesel Particulate Filter (DPF) regeneration have been developed to assist in the systematic and cost-effective optimization of next generation particulate trap systems. In the present study we employ an experimentally validated, state-of-the-art multichannel DPF simulator to study the regeneration process over the entire spatial domain of the filter. Particular attention is placed on identifying the effect of inlet cones and boundary conditions, filter can insulation and the dynamics of “hot spots” induced by localized external energy deposition. Comparison of the simulator output to experiment establishes its utility for describing the thermal history of the entire filter during regeneration. For effective regeneration it is recommended to maintain the filter can Nusselt number at less than 5.
Technical Paper

Multi-Instrumental Assessment of Diesel Particulate Filters

As different Diesel Particulate Filter (DPF) designs and media are becoming widely adopted, research efforts in the characterization of their influence on particle emissions intensify. In the present work the influence of a Diesel Oxidation Catalyst (DOC) and five different Diesel Particulate Filters (DPFs) under steady state and transient engine operating conditions on the particulate and gaseous emissions of a common-rail diesel engine are studied. An array of particle measuring instrumentation is employed, in which all instruments simultaneously measure from the engine exhaust. Each instrument measures a different characteristic/metric of the diesel particles (mobility size distribution, aerodynamic size distribution, total number, total surface, active surface, etc.) and their combination assists in building a complete characterization of the particle emissions at various measurement locations: engine-out, DOC-out and DPF-out.
Technical Paper

Multi-Functional Reactor for Emission Reduction of Future Diesel Engine Exhaust

Future diesel emission control systems have to effectively operate under non-conventional low-temperature combustion engine operating conditions. In this work the research and development efforts for the realization of a Multi-Functional catalyst Reactor (MFR) for the exhaust of the upcoming diesel engines is presented. This work is based on recent advances in catalytic nano-structured materials synthesis and coating techniques. Different catalytic functionalities have been carefully distributed in the filter substrate microstructure for maximizing the direct and indirect (NO2-assisted) soot oxidation rate, the HC and CO conversion efficiency as well as the filtration efficiency. Moreover, a novel filter design has been applied to enable internal heat recovery capability by the implementation of heat exchange between the outlet and the inlet to the filter flow paths.
Journal Article

Investigation of SCR Catalysts for Marine Diesel Applications

Evolving marine diesel emission regulations drive significant reductions of nitrogen oxide (NOx) emissions. There is, therefore, considerable interest to develop and validate Selective Catalytic Reduction (SCR) converters for marine diesel NOx emission control. Substrates in marine applications need to be robust to survive the high sulfur content of marine fuels and must offer cost and pressure drop benefits. In principle, extruded honeycomb substrates of higher cell density offer benefits on system volume and provide increased catalyst area (in direct trade-off with increased pressure drop). However higher cell densities may become more easily plugged by deposition of soot and/or sulfate particulates, on the inlet face of the monolithic converter, as well as on the channel walls and catalyst coating, eventually leading to unacceptable flow restriction or suppression of catalytic function.
Technical Paper

Further Experimental Study of Asymmetric Plugging Layout on DPFs: Effect of Wall Thickness on Pressure Drop and Soot Oxidation

In order to guide the development of asymmetric plugging layout Diesel Particulate Filters, hereafter referred to as “VPL-DPF”, in this paper we present some evaluation results regarding the effect of design parameters on the VPL-DPF performance. VPL-DPF samples which have different wall thicknesses (thin and thick walls) were evaluated in regards to their pressure drop and soot oxidation behaviors, with the aim to optimize the design of DPF structure. As a result of pressure drop evolution during soot loading, contrary to our expectation, in some cases, it was found out that VPL increases the transient pressure drop compared to the conventional plugging layout DPF. That meant there is an appropriate specific optimum wall thickness for adoption of VPL which has to be well defined at its structural design phase. Based on our previous research, it is expected that this result is due to interactions among the different (five) wall flows that exist in a VPL-DPF.
Technical Paper

Fundamental Studies of Diesel Particulate Filters: Transient Loading, Regeneration and Aging

Compliance with future emission standards for diesel powered vehicles is likely to require the deployment of emission control devices, such as particulate filters and DeNOx converters. Diesel emission control is merging with powertrain management and requires deep knowledge of emission control component behavior to perform effective system level integration and optimization. The present paper focuses on challenges associated with a critical component of diesel emission control systems, namely the diesel particulate filter (DPF), and provides a fundamental description of the transient filtration/loading, catalytic/NO2-assisted regeneration and ash-induced aging behavior of DPF's.